1. Field of the Invention
This invention relates to an ink-jet printer, and, in particular, to an ink supply system for use in an ink-jet printer. More specifically, the present invention relates to an ink supply system particularly suitable for use in an ink-jet printer of the type in which ink droplets are formed, selectively charged and deflected by an electric field.
2. Description of the Prior Art
FIG. 6 shows a prior art ink supply system for use in an ink-jet printer disclosed in Japanese Patent Laid-open Pub. No. 58-56867, assigned to the assignee of this application. As shown, the ink supply system includes a valve assembly 20 which is provided with an ink chamber 21 which, in turn, is in fluidic communication with an inlet port 22 at one end, with a discharge port 23 at the opposite end, and with an outlet port 24 in the middle. Within the ink chamber 21 is provided a horizontally elongated cylinder 30 for receiving therein a valve member, and the cylinder 30 may be moved reciprocatingly by a lever 40 which is pivotally supported at an O-ring 50. When a solenoid coil 80 is energized, a plunger 60 is pulled in the direction indicated by the arrow A, so that the cylinder 30 is caused to move in the direction indicated by the arrow A'. On the other hand, when the solenoid coil 80 is deenergized, the plunger 60 is pushed in the direction indicated by the arrow B by means of a return spring 70, so that the cylinder 30 is caused to move in the direction indicated by the arrow B'. In this manner, the cylinder 30 is moved back and forth within the ink chamber 21 depending on energization and deenergization of the solenoid coil 80.
Within the cylinder 30 are provided an inlet side valve member 31 provided with a rubber sheet 34, a discharging side valve member 32 provided with a rubber sheet 35 and a valve spring 33 extending between the two valve members 31 and 32. The inlet port 22 may be set open or closed depending on whether the rubber sheet 34 of the inlet side valve member 31 is brought into contact or out of contact with the inlet port 22. Similarly, the rubber sheet 35 of the discharging side valve member 32 may be brought into or out of contact with the discharging port 23 to set it open or closed. The inlet port 22 is in fluidic communication with an ink-jet nozzle head (not shown) via a tube of plastic or the like (not shown) and the discharging port 23 is in fluidic communication with an ink reservoir (not shown) via a tube of plastic or the like (not shown). The valve assembly 20 is typically mounted on a stationary frame of a printer or the like and it is fluidic communication with the ink-jet nozzle head mounted on a reciprocatingly movable carriage (not shown) via a plastic tube or the like.
Describing the operation of the valve assembly 20, FIG. 7a shows a condition when the valve assembly 20 is set in a closed state, wherein the inlet port 22 is closed by the valve member 31 and the discharging port 23 is set in fluidic communication with the ink chamber 21 so that the ink is discharged out of the ink chamber 21 into an ink reservoir (not shown). FIG. 7b shows a transitional state in which the valve assembly 20 changes from an off condition to an on condition, whereby the inlet and discharging ports are once closed at the same time temporarily. FIG. 7c shows when the valve assembly 20 is set in an open condition, wherein the inlet port 22 is set open and the discharging port 23 is closed, so that the ink supplied into the ink chamber 21 from the inlet port 22 is forwarded to the ink-jet nozzle head through the outlet port 24. Of course, the valve assembly 20 goes through the transitional state shown in FIG. 7b when it is changed from the on condition to the off condition.
In the valve assembly 20 described above, it is constructed as a separate unit and fixedly mounted on a frame of a printer. And, the inlet, discharging and outlet ports 22, 23 and 24 are provided as projecting outwardly from the body of the valve assembly 20. For this reason, there must be provided tubes for establishing fluidic connections between these ports 22, 23 and 24 to various other components, such as an ink reservoir, pump and ink-jet nozzle head. Such a structure is disadvantageous because the connection tubes are constantly set in motion due to the reciprocating motion of the carriage on which the ink-jet nozzle head is mounted, and, thus, the ink pressure inside of the tubes may vary, which could cause fluctuations in printed characters. Besides, such tubes are relatively long and thus large in pressure drops, which could result in slow response speed. Furthermore, there is an increased chance of drawing air into the ink-jet nozzle, which could cause unstability in the formation of ink droplets.